The present invention relates to a seal apparatus for sealing against a rod in a cylinder assembly such as a hydraulic cylinder for adjustment of a vehicle height, a hydraulic shock-absorber, etc.
In the above-mentioned cylinder assembly, a rod extends from an inside to an outside of a cylinder, and is slidably supported by a rod guide provided in the cylinder. For sealing a gap between the rod and the rod guide, in many cases, a double seal apparatus and an oil seal are arranged in the direction of the axis of the rod. The double seal apparatus comprises a rod seal which engages the rod, and a back-up ring which is provided radially outward of the rod seal to bias the rod seal toward the rod. A fluid which has leaked from an area between the rod and the rod seal is completely prevented from leaking to the outside, by means of the oil seal.
In the double seal apparatus, when axial compression of the back-up ring occurs due to the effect of the pressure of the fluid, the back-up ring radially expands and presses the rod seal against the rod. In order to prevent the application of an excessive force to the rod seal, a short partition wall is provided between the rod seal and the back-up ring. However, in the double seal apparatus in which the above-mentioned partition wall is provided, when the rod seal receives an axial-force due to the effect of the pressure of the fluid, the rod seal applies a force to the rod in an undesirable manner, which is caused by a dimensional error in production and thermal deformation of the partition wall and the rod seal.